Method for the production of alpha-naphthoquinones



Patented June 18, 1946 METHOD FOR THE PRODUCTION OF ALPHA-NAPHTHOQUINONES Julius Hyman and Carl Frederick Peters, Chicago, Ill., assignors to Velslcol Corporation, Chicago, Ill., a corporation of Illinois No Drawing. Application October 16, 1943, Serial No. 506,558

11 Claims. (01. 260-396) This invention relates to a novel improvement in the method for the oxidation of condensed ring aromatic hydrocarbons.

More particularly the present invention relates to an improved method for the manufacture of alpha naphthoquinones by direct oxidation of naphthalene and beta-substituted naphthalenes by hexavalent chromium at an increased yield and rate, and provides an important improvement over the heretofore general method first proposed by Groves in 1873 (Groves, Soc. 26, 209), who taught the formation of quinones by oxidizing a solution of a hydrocarbon, such as naphthalene. in glacial acetic with chromic acid (CrOs). Likewise, and more recently in the second edition (1941) of his Experiments in Organic Chemistry, Professor Louis F. Fieser, in describing the standard procedure for the production of condensed ring quinones, remarks (p. 2.32) "On oxidation with chromic acid naphthalene is converted largely into the phthalic acid, and even with the more careful control the reaction affords no more than 16% of alpha-naphthoquinone." The yield of 2-methyl-L4-naphthoquinone is given by Fieser as 38-42% of theoretical, and the yield of beta,beta-di-substituted naphthoquinones is given as 45-55%. 7

As distinguished from the foregoing heretofor standard procedure, the method of our present invention has enabled the obtaining of upward of 40% of alpha-naphthoquinone, 85-90% of 2- methyl-1,4-naphthoquinone and nearly quantitative yields of the beta-beta-di-substituted alphanaphthoquinones. 2,X-dimethyl 1.4 naphthoquinones, where X may represent position 3, 5, 6, 7 or 8, such as 2,6-dimethyl-1.4-naphthoquinone and 2,5-dimethyl-1,4-naphthoquinone,

may be prepared by our method in yields better than any obtained heretofore. Our method, as hereinafter more fully set forth, appears to be a general one for the manufacture in very good yield of the alpha-naphthoquinones. Furthermore, the proper arrangement and use of equipment can cut down the time of the preparation of the quinones over the older method very appreciably, and the reagents utilized in our process effect a further appreciable economy.

In general our present invention is characterized by and distinguished from the heretofore standard method in the use of a diluent for the hydrocarbon being converted, said diluent also acting as a solvent for the resulting condensed ring quinone reaction product, the diluent being a non-solvent for the oxidizing agent and inert with respect thereto. In this manner the diluent or solvent acts to separate the product from the oxidizing medium which would otherwise tend to oxidize a portion of it beyond the desired point, as is the case when using a mutual solvent, such as glacial acetic acid. As further distinguished from the prior use of glacial acetic acid (which may heat up beyond the point of product spoilage during the reaction), by proper selection of our solvent the reaction temperature is caused to be held to one favorable to rapid and controlled reaction.

Our invention relates specifically to the production of alpha naphtho-quinones by direct oxidation of naphthalene and beta substituted naphthalene hydrocarbons by the step which comprise intensively agitating the hydrocarbon in a diluent therefor of the class hereinbefore described together with an aqueous solution of a hexavalent water-soluble chromium compound while adding thereto a mineral acid. Upon completion of the reaction the solvent phase may be separated from the aqueous phase, and the quinone product recovered from the solvent.

As the diluent and solvent for both the condensed ring hydrocarbon and the resultant quinone reaction product we preferably employ carbon tetrachloride. since it shows good solvency for the product and boils at a temperature favorable to the rapid completion of the reaction, that is, it functions as a heat exchange medium in that it removes heat from the reaction mixture by boiling and thus the absorption of latent heat by the boiling solvent tends to hold the reaction under control and prevents product spoilage. As the solvent boils oiT it may be condensed and returned to the reaction mixture by means of a reflux condenser, or otherwise condensed and returned or collected separately. We may in the alternative employ other solvents such as for example benzene, although not with fully equivalent effect and results.

The amount of solvent used may be in proportion to either the desired yield or rate of reaction .or most economical balance between these factors. Thus with a higher proportion of solvent the higher will be the yield of quinone but the slower will be the rate of reaction.

As an oxidizing agent component We preferably employ sodium dichromate for reasons of economy although we may in the alternative'employ other hexavalent water-soluble chromium compounds such as chromic acid, potassium dichromate or ammonium dichromate. As the mineral acid component we preferably employ sulfuric acid in moderate dilution, such as sulfuric acid of from about 60 to about 77 weight percent concentration. In general the higher the concentration of theacid the more rapid will be the rate of reaction, but if too high concentrations of acid are employed, the yield of the product will be adversely affected. In the alternative we may employ other mineral oxy-acids, such as phosphoric acid.

Both the yield of reaction product and speed of reaction are favored by intensive agitation of the reaction mixture during the reaction. This is an important requirement in order to derive the most benefit from the process of our invention, and by observance of this requirement together with the other steps of our process the yield of quinone reaction product may be generally doubled over the former standard method and the time of completion of reaction may, if desired, be reduced to as much as one-tenth, or even less.

In carrying out the process, the hydrocarbon to be converted may be diluted with from about 5 to about 50 volumes of the diluent or solvent, and to this there is then added the requisite substantially stoichiometric proportion of chromium oxidizing component dissolved in water and the two solutions subjected to intensive agitation by a suitable stirring device extending into the reaction vessel. To this mixture there is then added, while continuing the agitation, the requisite amount of mineral acid to react with the chromium compound, or a slight excess thereof, so that, for example, when the acid used is suliuric acid any chromic oxide, (CraOs), formed is converted to chromic sulfate. We preferably use the acid in dilute form such as for example sulfuric acid of 77% by weight concentration. The acid is added to the other reactants gradually by suitable means, such as a dropping funnel, or similarly functioning device, the rate of addition or dropping depending on the extent of original dilution of the hydrocarbon, the efficiency of the reflux condenser in handling vaporized solvent, or the rate of return or re-addition of solvent when externally condensed.

When it desired to carry out the reaction at the most rapid rate, and consequently with a smaller proportionate amount of solvent, tendency to overheating due to the exothermic reaction may be controlled by subjecting the reaction vessel to external cooling to maintain the reaction temperature below 85 C. However, the tem perature of the reaction as previously indicated may be favorably controlled by means of the diluent either wholly when used in sufilciently large volume, or at least to a large extent with smaller volumes of solvent. Thus, for example, boiling carbon tetrachloride (which when alone boils at about 7677 C.) acts as a heat exchange medium, by removing heat from the reaction mixture, thus holding the reaction under control. The solvent vapors are suitably condensed and returned to the reaction mixture.

After al1 of the acid has been added the temperature of the reaction mixture is maintained at about 70 C. for a period of from about one to two hours to insure completion of the reaction after which agitation is discontinued, the mixture cooled and as much of the solvent phase or layer as possible is separated by decanting. To effect further separation, water and additional solvent is added to the remaining mixture, the mixture stirred for a short time and the solvent layer permitted to settle to the bottom and separated and added 'to the first separated solvent layer and filtered for clarification. The solvent 4 is then distilled oil? from the quinone reaction product in a vacuum, and the quinone further concentrated to cause crystallization. The crystalline material may be subjected to further high purification by sublimation.

The following examples are introduced for the purpose of illustrating our invention but should not be considered as undue limitations of the broader scope of our novel process:

Example 1 Dissolve 100 grams of beta-methyl naphthalene in 500 grams of carbon tetrachloride. Dissolve 500 grams of commercial sodium dichromate in 175 grams of hot water. Pour these two solutions into a 3-liter 3-necked flask, equipped with an eilicient stirrer, a reflux condenser, and a dropping funnel. The flask should be surrounded by a water bath held at 50 C. After the stirrer has been started and the contents of the flask agitated as violently as possible, add (through the dropping funnel) 896 grams of 77% (by weight) sulfuric acid, the rate of dropping depending on the efficiency of the reflux condenser in handling the vaporized carbon tetrachloride. Should the reaction tend to get out of hand due to overheating, cold water should be run into the water bath. After the addition of acid has been completed, keep the water bath at 70 C., for 1 /2 to 2 hours. Then stop the agitation, cool the mixture and decant therefrom as much of the carbon tetrachloride layer as pomible. Pour water into the flask; add 100 grams more of carbon tetrachloride and stir for an additional ten minutes. The carbon tetrachloride layer will now settle to the bottom. The acid layer can be decanted and discarded, or worked up for those components desired. A complete separation of the acid from the carbon tetrachloride is efiected by means of a separatory funnel. All of the carbon tetrachloride solutions are pooled and filtered to clarity through filter paper.

The carbon tetrachloride may be distilled ofi from the quinone in a vacuum, using a water bath heated to 50 C. The quinone is concentrated to a point where crystallization begins. Thereupon the concentrated solution is transferred to a beaker and allowed to crystallize at room temperature. Further crops of crystals are obtained by allowing the mother liquor to cool in an icebox, or by reducing it still further. If the beta-methyl naphthalene starting material was pure, the 2- methyl-1,4-naphthoquinone obtained will have a melting point of 100-104 C., without further purification. Vacuum sublimation has been found most effective to produce quinones of a very high purity. It may, on the other hand, be sufiicient to use the carbon tetrachloride solution of the pro-vitamin K (Z-methyl-lA-naphthoquinone) for further reactions or purposes.

Example 2 Repeat the method of Example 1 but substitute grams of naphthalene for the grams of beta-methyl naphthalene mentioned previously. The product obtained will then be alpha-naphthoquinone.

Example 3 Substitute grams of 2,6-dimethyl naphthalene for the 100 grams of beta-methyl naphthalene mentioned in Example 1. The product of the reaction will be 2,6-dimethyl-l,4-naphthoqumone.

3 grams of beta-methyl naphthalene is dissolved in 180 grams of carbon tetrachloride. To this is added grams of commercial sodium dichromate dissolved in 6 grams of hot water. The above solutions are placed in a 1-liter 3-necked flask equipped with an efilcient stirrer, a dropping funnel, and a distilling condenser of large bore. The mixture is agitated energetically, and grams of 77% sulfuric acid added through the dropping funnel. The time of addition need not be over seconds. The flask is not subjected to exterior cooling, as the distilling carbon tetrachloride should hold the heat to the proper temperature, which should not exceed 85 C. After five minutes the reaction may be discontinued and the product handled similarly to the method outlined in Example 1. The yield of 2-methyl- 1,4-naphthoquinone will be around 80% of theoretical by the use of this rapid method.

We claim as our invention:

L'The method of producing alpha-naphthoquinones by direct oxidation of a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises subjecting the hydrocarbon in the presence of a diluent therefor to oxidation by means of an aqueous solutionof a hexavalent water-soluble chromium compound and a mineral acid as the oxidizing agent while intensively agitating said reactants, said diluent being a non-solvent for said oxidizing agent and inert with respect thereto and being a solvent for the resulting condensed ring quinone reaction product.

2. The method of producing alpha-naphthoquinones by direct oxidation of a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises subjecting the hy-. drocarbon diluted with carbon tetrachloride to oxidation with an aqueous solution 01' a hexavalent water-soluble chromium compound and a mineral acid.

3. The method of producing alpha-naphthoquinones by direct oxidation of a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises intensively agitating a mixture of the hydrocarbon diluted with carbon tetrachloride and an aqueous solution of a hexavalent water soluble chromium compound while adding thereto sulfuric acid, and recovering the resultant condensed ring quinone reaction product from solution in the carbon tetrachloride.

4. The method of producing alpha-naphthoquinones by direct oxidation oi. a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises intensively agitating a mixture of the hydrocarbon diluted with "carbon tetrachloride and an aqueous solution oi. sodium dichromate while adding thereto sulfuric acid.

5. The method of producing alpha-naphthoquinones by direct oxidation 01. a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises subjecting the hydrocarbon in dilution with carbon tetrachloride to oxidation by i'i'itensively agitating therewith an aqueous solution 01' a hexavalent water-soluble chromium compound and dilute sulfuric acid.

6. The method of producing alpha-naphthoquinone which comprises diluting naphthalene with carbon tetrachloride, mixing therewith an aqueous solution of sodium dichromate, and adding sulfuric acid to the mixture while subjecting the reactants to intensive agitation, separating from the reactants a carbon tetrachloride solvent phase and removing alpha-naphthoquinone from solution therewith.

7. The method ofproducing 2-methyl-1,4- naphthoquinone which comprises diluting betamethyl naphthalene with carbon tetrachloride, mixing therewith an aqueous solution of sodium dichromate, and adding sulfuric acid to the mixture while subjecting the reactants to intensive agitation, separating from the reactants a carbon tetrachloride solvent phase and removing 2 methyl 1,4 naphthoquinone from solution therein.

8 The method of producing a 2,X-.dimethyl- 1,4-naphthoquinone from a 2,X dimethyl naphthalene, where X represents position 3, 5, 6, 7 or 8, which comprises diluting the latter with carbon tetrachloride, mixing therewith an aqueous solution of sodium dichromate, and adding sulfuric acid to the mixture while subjecting the reactants to intensive agitation, separating from the reactants a carbon tetrachloride phase and removing the 2,X-dimethyl-1,4-naphthoquinone reaction product from solution therein.

9. The method 01' producing2,6-dimethyl-1,4- naphthoquinone which comprises diluting 2,6-61- methyl naphthalene with carbon tetrachloride, mixing therewith an aqueous solution oi. sodium dichromate, and adding sulfuric acid to the mixture while subjecting the reactants to intensive agitation, separating from the reactants a carbon tetrachloride solvent phase and removing 2,6-

dimethyl 1,4 naphthoquinone from solution therein.

10. The method 01' producing alpha-naphthoquinones by direct oxidation or a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises subjecting the hydrocarbon diluted with benzene to oxidation with an aqueous solution oi. a hexavalent watersoiuble chromium compound and a mineral acid.

11. The method of producing alpha-naphthoquinones by direct oxidation of a condensed ring aromatic hydrocarbon selected from the group consisting of naphthalene and beta-substituted naphthalenes which comprises subjecting the hydrocarbon in the presence of a diluent therefor selected from the group consisting 01' carbon tetrachloride and benzene to oxidation with an aqueous solution 01' a hexavalent water-soluble chromium compound and a mineral acid.

JULIUS HYMAN.

CARL FREDERICK PETERS. 

